Spray nozzle with improved tip and method of manufacture

ABSTRACT

The invention provides a compact spray nozzle having an improved tip for reproducibly forming droplets from small amounts of liquid with improved operational stability and spray pattern quality compared to prior art atomizing devices. The invention further provides a method for manufacturing the nozzle tip by machining comprising the step of machining the orifice and the inner section and/or the centering section in one setup.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

FEDERALLY SPONSORED RESEARCH

Not Applicable

SEQUENCE LISTING OR PROGRAM

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a spray nozzle having an improved tipand its method of manufacture for providing a repeatable performance interms of droplet size and spatial droplet distribution. The invention isparticularly suitable for the fine atomization of small amounts ofliquids.

2. Background of the Invention

Spray nozzles are used to spray small amounts of liquids in variousapplications, such as medical nebulizers, chemical analysis of liquidsamples, spray drying and coating medical devices.

Such spray nozzles generally comprise a body with a liquid line and aremovable tip having a central orifice provided at the atomizing end,which extends to an inner section. The spray nozzle may also include oneor more passages for an atomizing fluid, which may be expelled throughan annular gap or gas annulus provided between the body orifice and thetip orifice to disintegrate the liquid. Spray nozzles using compressedgas to disintegrate a liquid are also referred to as twin-fluid nozzles.

Optimum atomization and particle transport efficiencies generallydepends on the spatial characteristics of the spray plume and on thedroplet size which, in turn, depends on the roundness of tip orifice andconcentricity between the tip orifice and inner section. This isparticularly true, when an atomizing gas is provided through acomparatively small annular gap, which often has a width on the order ofonly 20 to 250 micrometers.

However, the lack of concentricity between the inner section and orificeof the tip is a common problem of prior art spray nozzles havingcomparatively small orifices. FIG. 1 depicts an enlarged view of a tipof an exemplary spray nozzle having a conical inner section extending toan orifice. It can be seen that the orifice 16 of the tip 3 is notconcentric with respect to the inner surface 72 of the tip. In thisexample there is an eccentricity of 0.04 mm between axis of innersection 71 and axis of tip orifice 70.

Inner section-orifice eccentricity may result from machining the orificeand inner section of the tip in different setups. A further problemassociated with conventional atomizing devices are imperfections of theorifices in terms of roundness and surface quality. The orifices aregenerally manufactured using conventional manufacturing procedures suchas drilling. For instance, drilling of small holes can lead to spiralmarks and burrs and may require secondary procedures such aselectropolishing which, in turn, may result in manufacturing tolerancevariations and/or out-of-roundness of the orifice. When manufacturing aseries of spray nozzles comprising comparatively small orifices usingcurrent machining procedures the reproducibility within a badge maytherefore not be assured. In addition, with current spray nozzles thereis a risk of misalignment during disassembling and reassembling of thenozzle resulting in poor concentricity of the body in relation to thetip orifice. Thus, devices, even of the same type, often will havedifferent spray characteristics resulting from very minor variations interms of concentricity of tip orifice and inner section, orificeroundness and surface quality. To visualize the effect of aneccentricity between inner section of tip and tip orifice on the spraycharacteristics of a twin-fluid nozzle, the velocity distribution of thefluid exiting the tip orifice has been simulated using ComputationalFluid Dynamics (CFD) software. FIG. 2A is a scalar representation andFIG. 2B is a vector representation of the fluid exiting the annular gap.Despite the optimum roundness and equal width of the tip orifice, thereis an inhomogeneous velocity distribution at the annular gap, which iscaused by a small eccentricity between the inner section of the tip andthe tip orifice.

The spray performance in terms of symmetric spatial droplet distributionand tight droplet size distribution of spray nozzles is closely relatedto the roundness and concentricity of tip orifice and inner section oftip. In case of twin-fluid atomizers, any imperfection and eccentricitybetween the axes of the liquid orifice and the tip can cause the flow ofthe atomizing gas to be cylindrically asymmetric with respect to theaxis of the liquid exiting from the liquid orifice. Hence, inhomogeneousgas velocities within the annular gap, as illustrated in FIGS. 2A and2B, will lead to nebulization by the atomizing gas that is different ondifferent sides of the spray plume. Consequently, poor spray stabilityand droplets that are too large and polydisperse in size may result inpoor reproducibility and often poor stability during operation which, inturn, may lead to coating defects or reduced sample analysis efficiency.

OBJECT OF THE INVENTION

Accordingly, there is a need for a spray nozzle comprising an improvedtip to atomize small liquid amounts that overcomes the aforementionedproblems with the prior art and provides a homogeneous spatial dropletdistribution, a tight droplet size distribution and an improvedstability and reproducibility of precision spraying processes.

One object is to provide a spray nozzle to atomize small liquid amountshaving a compact and robust design that can be manufacturedreproducibly, resulting in a repeatable performance from one spraynozzle to the next.

Another object is to provide a spray nozzle, which ensures theconcentric alignment of the body in relation to the tip to reproduciblygenerate a uniform spray pattern.

Yet another object is to provide a cost-effective manufacturing methodfor machining the tip orifice, the inner surface of the tip and thecentering section between nozzle body and tip.

Still another object is to allow repeatable assembling and disassemblingof the tip and thereby ensuring proper alignment of the tip orificerelative to the body.

These and additional features and advantages of the invention will bemore readily apparent upon reading the following description ofexemplary embodiment of the invention and upon reference to theaccompanying drawings herein.

SUMMARY

In one embodiment, a device to disintegrate a liquid into fine dropletsis provided comprising a body having an entrance end and an exit end fora first fluid and a tip having an inner section extending to an orificethrough which a second fluid is expelled. The tip is provided at theatomizing end and essentially coaxial with the body such that anintermediate space is formed between the body and tip. At least aportion of the inner section of the tip is machined in the same setup asthe orifice so that the axis of the orifice is concentric with the axisof the machined inner section. In certain embodiments, the tip may bemachined by internal turning and the orifice diameter of the tip may besmaller than 2 mm. Also, the machined portion of the inner section maybe used to align the tip in relation to the body. The tip may furthercomprise a centering section to align the tip in relation to the bodybeing machined in the same setup as inner section and orifice of tip.The inner section of the tip may have a conical shape. The first fluidmay be a liquid and the second fluid a gas. Alternatively, the firstfluid may be a gas and the second fluid a liquid.

In a further embodiment, a device to disintegrate a liquid into finedroplets is provided comprising a nozzle tip having an inner sectionextending to an orifice that is smaller than 2 mm through which thefluid is expelled, wherein at least a portion of the inner section ismachined in the same setup as the orifice so that the axis of theorifice is concentric with the axis of the inner section. In certainembodiments, at least a portion of the inner section is machined byinternal turning.

In another embodiment, a method is provided for manufacturing a nozzletip having an inner section extending to an orifice with an diameter ofup to 2 mm, comprising the step of machining the orifice and at least aportion of the inner section of the nozzle tip in the same setup byinternal turning so that the axis of the orifice is concentric with theaxis of the inner section.

In still another embodiment, a method for manufacturing a device todisintegrate a liquid into fine droplets having a body with a centeringsection and a tip with an orifice diameter up to 2 mm, comprising thesteps of machining the tip orifice and at least a portion of thecentering section of the tip in the same setup by turning so that theaxis of the orifice is concentric with the axis of the centering sectionof the tip and assembling the body and the tip such that the centeringsection of the tip mates with the centering section of the body.

DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, serve to explain the principles of theinvention. The drawings are in simplified form and not to precise scale.

FIG. 1 (Prior Art) is a longitudinal cross-sectional detail view of anozzle tip comprising an orifice and an inner section;

FIG. 2A (Prior Art) is a Computational Fluid Dynamics simulation (scalarrepresentation) of the velocity distribution at an nozzle orifice;

FIG. 2B (Prior Art) is a Computer Fluid Dynamics simulation (vectorrepresentation) velocity distribution at an nozzle orifice;

FIG. 3A is a longitudinal cross-sectional view of an twin-fluidatomizer;

FIG. 3B is a longitudinal cross-sectional expanded view of the atomizertip of FIG. 3A;

FIG. 4A is a longitudinal cross-sectional view of the atomizer tip ofFIG. 3 showing the machining path during a turning operation;

FIG. 4B is a expanded view of the atomizer tip of FIG. 3;

FIG. 5 (Prior Art) is a spatial droplet distribution generated by aconventional spray nozzle; and

FIG. 6 is a spatial droplet distribution generated by the spray nozzleof the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS/PREFERRED EMBODIMENTS

The invention provides a compact spray nozzle for reproducibly formingdroplets from small liquid amounts comprising a tip with improvedaccuracy providing improved operational stability and reliabilitycompared to prior art atomizing devices. The spray nozzle has a bodycomprising a central fluid line for the fluid to be disintegrated and atip having a central orifice provided at the atomizing end. The tip isremovably secured and aligned through a centering section, so that aconcentric alignment between the body and the tip orifice and arepeatable assembly and disassembly can be provided.

The spray nozzle may also include one or more passages for an atomizingfluid, which is expelled through an annular gap or gas annulus providedbetween the body orifice and the tip orifice to disintegrate the liquid.The spray nozzle is designed to allow precise and repeatable machiningof the inner surface of the tip, the centering section between tip andbody and the tip orifice to ensure optimized concentricity and surfacequality of the atomizing end.

The invention further provides a method for manufacturing the nozzle tipby machining the orifice and the inner section and/or the centeringsection in one setup.

DETAILED DESCRIPTION

While the invention will be described in connection with certainembodiments, it will be understood that the invention is not limited tothese embodiments. On the contrary, the invention includes allalternatives, modifications and equivalents as may be included withinthe spirit and scope of the present invention. Details in theSpecification and Drawings are provided to understand the inventiveprinciples and embodiments described herein, to the extent that would beneeded by one skilled in the art to implement those principles andembodiments in particular applications that are covered by the scope ofthe claims. All dimensions used herein are suggestive and not intendedto be restrictive.

FIG. 3A is a longitudinal cross-sectional view of an exemplary spraynozzle or atomizer of the present invention. An expanded view of the tipregion of the nozzle is provided in FIG. 3B.

The atomizer comprises body 2 and tip 3 being secured to the atomizingend to permit passage of gas. The body includes a central fluid line,which extends from the fluid inlet 4 to the fluid orifice 15. Thediameter of orifice 15 may range between approximately 0.05 and 0.5 mmdepending on the particular application. The tip 3 is secured bysecuring ring 8 such that a small annular gap 16 to permit passage ofgas therethrough from the fluid passages 6 is provided between the tiporifice and body. It has preferably a tapered inner section extending toa central orifice 16. Alternatively, the inner section of the tip mayhave a hemispherical or cylindrical shape. The diameter of the tip ofthe body and the orifice diameter of the tip defines the width of theannulus. The nozzle body is preferably made from a metallic materialsuch as stainless steel. Alternatively, a polymeric material such asPEEK can be used. The tip is preferably made from a metallic materialsuch as stainless steel, titan and the like. Other tips with variousgeometries may be provided to adapt the atomizer for specificapplications. The tip may further comprise additional bores to providevarious spray patterns such as a flat spray. The atomizer is connectedvia fluid inlet 4 to means to supply the liquid to be atomized such as apump coupled to a supply container and via fluid inlets 5 to means tosupply the atomizing gas.

In operation, the liquid to be atomized is supplied through the inlet 4.The atomizing fluid (compressed gas) is fed in the inlets 5, travelsthrough the passages 6 extending from fluid inlets 5 via a portionsubstantially coaxial to the liquid line and a conical portion and exitsthe atomizer trough the annular gap 16. The liquid flows from fluidinlet port 4 through the fluid line to the atomizing end and exitsorifice 15. The liquid is disintegrated into fine droplets by theatomizing gas when it exits orifice 15. Liquid and carrier gas is mixedoutside the atomizer to obtain an aerosol.

In an further embodiment, the liquid to be atomized may be suppliedthrough the fluid inlet, travel through the fluid passages extendingfrom fluid inlet via a portion substantially coaxial to the fluid lineand a conical portion and exit the atomizer trough the annular gapformed between the body orifice and tip orifice. The atomizing fluid(compressed air) may flow from one or more fluid inlet ports through aninner fluid line to the atomizing end of the nozzle body where it exitsthe orifice.

In still another embodiment, electrostatic means may be furthermoreprovided to assist the liquid disintegration process. A high voltagesource may be electrically connected to the liquid conduit of thenozzle, while portions of the nozzle are electrically isolated from theliquid conduit.

To ensure that the center of the fluid orifice 15 runs coaxial to thecenter of the annular gap 16 there is provided a centering section toalign the tip in relation to the body, as depicted in FIG. 3B by arrow7. Thus, tip 3 can be easily removed for maintenance and cleaning of theatomizer without the risk of misalignment between the tip and body.

To maximize surface finish and concentricity, the followingmanufacturing procedure is adopted. In a first step, a central bore isdrilled having a smaller diameter than the finished orifice. Next, asillustrated in FIG. 4 tip orifice 16, inner surface 72 and centeringsection 35 are machined in one setting. Tip orifice 16 and inner surfaceof the tip may be machined by internal turning and centering section 35by external turning. Alternatively, the inner surface of the tip and theorifice may be machined by grinding or by boring out.

FIG. 4A is an enlarged view of an exemplary atomizer tip 3 during thefinal machining operation shown in more detail in FIG. 4B. The finalmachining path or machined section of the inner surface of the atomizertip is illustrated by line 73. A small bore tool 75 having cutting edge74 may be used to perform the machining operation. Machined section 73extends from the inner tapered section to the orifice. Thus, a smoothtransition between the tapered section of tip and tip orifice 16 isprovided. By machining the inner surface of the tip 72 including the tiporifice in one setup a superior quality is obtained in terms ofconcentricity, roundness and smooth finish of inner section and orificeof tip as well as annular gap. In addition, a secure connection andoptimized alignment between body orifice 15 and tip 3 is provided. Theconcentricity between the axis of body orifice 15 and the axis oforifice 16 of tip 3 is substantially optimized compared to prior artatomizers.

A repeatable and cost-effective manufacturing method of the nozzle tipis provided by machining the sections that are critical for the sprayperformance in the same setup. Thus, timesavings and an improvedaccuracy of the atomizer can be achieved compared to machiningoperations comprising several setups.

In order to demonstrate the performance of the spray nozzle of thepresent invention various spray tests have been conducted. The spatialdroplet distribution of the twin-fluid nozzle, depicted in theembodiment of FIG. 3, has been measured and compared to an exemplarytwin-fluid nozzle known by the prior art. The prior art nozzle has anannular hap with a homogeneous width and a small eccentricity betweenaxis of inner section and axis of tip orifice as shown in FIG. 1. Thespray pattern was measured 20 mm downstream from the nozzle orificeusing an Optical Patternator. The liquid to be atomized (DI Water) wassupplied by a syringe pump (manufactured by Hamilton Company, Reno,Nev.) at a flow rate of 15 ml/h. The gas was fed into the atomizingdevice at a pressure of 0.7 bar.

FIG. 5 depicts the spray pattern of the prior art spray nozzle. Thespray pattern has an asymmetric spray distribution comprising coarseparticles in the right portion. The asymmetric spray distributionresults from inhomogeneous gas velocities within the annular gap causedby the error in concentricity between the tip orifice and inner sectionas discussed before.

In contrast, the spray pattern of the atomizer of the present inventionhas a homogeneous spatial droplet distribution as depicted in FIG. 6.

The results outline the advantages of the design and manufacturingmethodology of the atomizer of the present invention in terms of spraypattern quality. The liquid atomization process has been improved byoptimizing the atomization region in terms of concentricity between tiporifice and inner section of tip and concentricity between the axis ofbody and the axis of tip. In addition, there is provided an improvedsurface quality and a securing mechanism that prevents misalignment.Thus, a homogeneous spray pattern having a homogeneous dropletdistribution can be obtained.

1. A method for manufacturing a tip of a micro nozzle for producing a spray with a homogenous spatial droplet distribution having an orifice with a diameter of up to 2 mm and an inner section extending to the orifice comprising the steps of: forming a central cavity within the tip having a smaller size in the orifice section than the finished orifice; and performing a shaping operation of the orifice and of at least a portion of the inner section extending to the orifice in the same setup, whereby a smooth transition between the orifice and the inner section extending to the orifice is obtained and the longitudinal axis of the orifice is substantially concentric with the longitudinal axis of said portion of the inner section extending to the orifice so that the error of concentricity is less than 0.02 mm.
 2. The method according to claim 1, wherein the inner section is used to align the tip in relation to a micro nozzle body.
 3. The method according to claim 1, wherein the tip further comprising a step of shaping a centering section to align the tip in relation to a micro nozzle body.
 4. The method according to claim 1, wherein the inner section of the tip extending to the orifice is conically shaped.
 5. The method according to claim 1, wherein the shaping operation of the orifice is performed by internal turning.
 6. The method according to claim 1, wherein the shaped portion of the nozzle tip is used as centering section to align a micro nozzle body and the tip.
 7. The method according to claim 1, wherein the orifice is shaped so that an annular gap between 20 and 250 micrometers is formed between a micro nozzle body and the tip.
 8. The method according to claim 1, wherein the portion of the inner section of the tip leading to the orifice and the orifice are shaped by turning.
 9. The method according to claim 1, further comprising the step of using the micro nozzle for reproducibly forming droplets from small liquid amounts by feeding a first fluid into an entrance end of a body and a second fluid into an intermediate space extending to an annular gap formed between body and tip and disintegrating the liquid.
 10. The method according to claim 9, wherein the first fluid is a liquid and the second fluid is a gas.
 11. The method according to claim 9, wherein the first fluid is a gas and the second fluid is a liquid.
 12. The method according to claim 9, further comprising the step of using electrostatic means to disintegrate the liquid.
 13. The method according to claim 9, wherein the spray is applied to a medical device to form a coating.
 14. The method according to claim 9, wherein the spray is dried to form particles. 